The subject matter disclosed herein relates generally to superconducting magnets, and more particularly to systems and methods for cooling superconducting magnets.
Superconducting coils, for example superconducting coils forming Magnetic Resonance Imaging (MRI) magnets, are cryogenically cooled using a helium reservoir. The cryogen cooling system of some of these MRI systems include a coldhead that operates to recondense vaporized cryogen to continually cool the superconducting magnet coils during system operation.
Additionally, these MRI magnets can experience large axial and radial electromagnetic (EM) forces during coil energization. In MRI systems, the magnet coils can be self-supporting in the radial direction. However, in the axial direction, because of the significant inter-coil forces, the magnet coils need to have support at the coil flanges through the interface with a support structure (e.g., coil former).
When the magnet coils are expanding radially, such as during energization, frictional heat is generated and released due to stick-slip motion between the coil support and the magnet coils. The generated heat can overheat a localized area of the coil and create a normal zone, where the conductor loses superconducting property and transfers to a normal resistive state. The normal zone will spread through the coil due to the Joule heat and the thermal conduction, which results in a quench event. The quench is accompanied by the rapid boil-off of helium escaping from the cryogen bath in which the magnet coils are immersed. Each quench, followed by the re-fill and re-ramp of the magnet, is an expensive and time consuming event.
Different devices and methods have been used to cool the coils during start-up and steady state operation. For example, different conduction cooling methods have been used. However, these conduction cooling methods are inefficient.